JHU BME 580.422 Biological Systems II
Brain and Behavior
Reza Shadmehr
Regions of the cortex specialize in aspects of control of perception
and action
1.
2.
3.
Principle of contralateral control of action
Language centers
Centers for perception of visual information
In 1870, it was discovered that when one electrically stimulates the cortex of a
dog, movements occur with the contralateral limb.
• Hints of localization of function: stimulation in the frontal lobe most easily and
•
repeatedly produced limb movements.
• Wada test: When a patient is about to undergo neurosurgery, in some cases a
procedure is performed to better understand the function of each hemisphere. A
drug is injected into the carotid artery that supplies blood to one hemisphere.
This effectively shuts down that hemisphere, paralyzing the opposite side of the
body.
• If the language centers are on the right side, the patient will be unable to speak
if that side is affected. The procedure lasts for a couple of minutes and then is
washed out.
Principle of contralateral control: each cerebral hemisphere controls
movements of the opposite side of the body
The “Wada” test
Before injection
After injection in the
right carotid artery
Injection of anesthetic (sodium amobarbital) in the right internal carotid artery. When the right carotid artery is
injected, the right cerebral hemisphere is inactivated, paralyzing the left side of the body. Note that the
examiner is holding an object in hand. He is asking the patient to name the object.
Study of language as a window to localization of function in the brain
Broca’s area: A place in the brain that is critical for producing language.
Paul Broca
(1824-1880)
The brain of patient Leborgne, known as “Tan”.
Study of language as a window to localization of function in the brain
Wernicke’s area: A place in the brain that understands spoken or written
language.
Karl Wernicke (1848-1904)
found patients that could
speak, but failed to
comprehend language.
Kandel et al. (2000) Principles of Neural Science
Study of vision as a window to localization of function in the brain
Area V4: perception of color
Area MT: perception of motion
Area TEO: perception of faces
Memory and the human brain: stimulation experiments
Neurosurgeon Wilder Penfield in 1950s applied electrical currents to
different areas of the brain during surgery in epileptic patients.
He found that stimulation of points in the temporal lobe produced vivid childhood
memories, or pieces of old musical tunes.
A 21 year old man reported: “It was like standing in the doorway at [my] high school. I
heard my mother talking on the phone, telling my aunt to come over that night.”
Another patient: “My nephew and niece were visiting at my home … they were getting
ready to go home, putting on their coats and hats … in the dining room … my mother was
talking to them.” (Penfield and Perot, Brain 86:595, 1963)
Places where stimulation evoked memories
R. Carter (1998) Mapping the Mind
R. Carter (1998) Mapping the Mind
Memory and the human brain: patient HM
27 year old assembly line worker who had suffered from untreatable and debilitating
temporal lobe seizures for many years. Surgeon removed medial portion of the temporal
lobes bilaterally.
H.M.’s seizures were improved, but there was a devastating side effect: he could no longer
form long-term memories.
After recovery from surgery, he maintained his vocabulary and language skills, maintained
his high IQ, and ability to recall facts about his life that preceded the surgery:
• could remember job that he held, where he had lived, and events of
childhood.
R. Carter (1998) Mapping the Mind
• normal immediate memory: he could retain a number for a short
period of time. He could carry on a conversation.
• could not recognize people that he had talked to just the day before
at the hospital. He did not what he ate at his last meal.
Corkin, Seminars in Neurology 4:249-259 1984.
Immediate memory is intact in amnesia. However, what is lost is the
ability to translate immediate memory into long-term memory.
Delayed paired-comparison task in HM
Clicks, flashes, tones, or hues were
presented to HM and then some
seconds later, the same or another cue
was presented and he was asked to
determine whether the two stimuli were
the same or different.
Amnesia spares old memories
When the hippocampus is damaged, the
patient does not lose the very old memories
that were acquired long ago (more than 6-10
years before the damage). Rather, the
damage reduces the ability of the brain to
maintain memories from the near the time of
the damage, and since the damage.
Healthy controls
Hippocampal damage
Recall performance on a test of news events that occurred from 1951 to 2005. The scores for six patients with damage
limited primarily to the hippocampal region and 13 controls have been aligned relative to the onset of amnesia. The data point
at –5 represents 1–5 years before amnesia, the point at –10 represents 6–10 years before amnesia, and so on. Error bars
indicate SEM.
Bayley, Hopkins, Squire (2006) J Neurosci 26:13311.
Amnesic patients show near normal ability to learn and store a motor skill.
While viewing hand in mirror, H.M. tries to trace between the
two lines. Number of errors refers to times that the border was
crossed.
• Could learn to do mirror writing: performance would
improve with practice and remain good on next day,
despite no conscious recall of prior practice.
Lesions of the temporal lobe appear to affect forms of
learning and memory that require a conscious record, and
are called declarative memories.
Kandel et al. Principles of Neural Science 2000 (62-2)
What we learn from patient H.M.
• The ability to acquire new memories about facts, episodes of our lives, places
that we have been, people that we know, etc. (declarative memories) is a
function of the medial temporal lobe.
• The medial temporal lobe is not required for immediate memory.
• The medial temporal lobe is not the ultimate location where declarative
memories are stored because H.M. can remember his childhood.
• Certain other memories (e.g., motor skills) can be learned normally without the
medial temporal lobe. In that case, the amnesic patient knows how to do a task
at an expert level but will claim that they have never done the task before.
Memories slowly become resistant to disruption: consolidation
• Deeply depressed patients were admitted to the hospital for electroconvulsive therapy.
• Before and after treatment, they were tested for their memory of TV programs that had
been broadcast for a single season during one of the preceding 16 years. Experiment was
performed in 1974.
• Before treatment, depressed patients
remembered programs that had been
broadcast recently better than older
programs.
• After treatment, patients remembered
the remote past normally, but their
memory was poor for recent 1-3 years.
(chance is 25%)
Squire and Kandel, Memory: from mind to molecules, 1999, p. 102
Jerry Levy (1986) Brain asymmetry: facts and
fallacies in statistical inference.
Brain Cognition. 5(1):115-25.
Summary
• The CNS is anatomically divided into seven regions: spinal cord, medulla,
pons, cerebellum, midbrain, diencephalon, and cerebral cortex
• The cortex has distinct functional regions: occipital lobe is for vision,
temporal lobe houses audition and vision for perception (what is it?), parietal
lobe houses vision for action (where is it?), frontal lobe houses the motor
cortex.
• Movements are controlled by the hemisphere contralateral to the limb.
• Language functions are usually in the left hemisphere, whereas face
recognition usually depends on the right hemisphere.
• There are distinct memory systems in the brain. Damage to the medial
aspect of the temporal lobe causes amnesia, where immediate memory is
intact, but the person cannot remember events of more than a few minutes
ago. Medial temporal lobe is a sort of “gateway” to memory of facts and
events. Motor memory does not depend on the medial temporal lobe.